thoughts on separated geometry
The line is being caused by a &quot;crease&quot; which is the result of 2 edges being too close together on a curved surface. Although the inner edge is necessary for the geometry of the &quot;top part&quot;, it is interfering with your mesh where the geometry is not needed.
One thing you could do is grab a section of the inner edge in the middle of each &quot;gap&quot; and edge slide (G + G) it so it pulls the second edge away from the first where they don't need to be close together. There may still be some artifacts in the corners though (circled in yellow), and if this ends up looking too incorrect, you may be best going with 2 separate pieces.